At one school, only two of 106 pupils entered for the AQA GCSE foundation tier, which carries a top C grade, achieved that mark.
Another said that all eight schools in her area had reported results were below expectations. A third teacher said the school was dropping compulsory languages because grades were so disappointing this year. French results nationally fell this year.
However, the AQA board denied any injustice. Changes to the mark scheme had occurred across many subjects and all three boards, and schools had had the chance to appeal.
Some 167,000 candidates sat AQA's main French GCSE this year. The controversy comes after changes this year to the way papers, covering the four skills of speaking, listening, reading and writing, are assessed and marks aggregated into final grades.
In French, pupils can be entered for each of four papers at one of two levels: foundation and higher. Foundation offers pupils a chance of a C.
Higher-tier covers those aiming at an A or B. This year, foundation candidates' marks in individual papers were converted to a uniform scale of 0-59. They had to score 200 across the four papers to gain a C overall.
Schools say foundation pupils found it hard to score more than 50 on any paper. As a result, a score below 50 in any paper was likely to result in missing a C overall.
A letter sent by the board to one school appeared to reveal that the standard was tougher this year.
Some schools claim the problems have been compounded this year by unusually low marks for pupils in the oral paper and that German was also affected.
A head of languages at a Lancashire secondary, said only two of his 106 foundation French candidates got a C. He said: "We don't expect exam boards to make things easy. But I think with AQA, people have not done as well as in previous years."
AQA was unable to give figures for numbers of foundation papers taken and C grades. George Turnbull, the board'sspokesman, said changes to the mark scheme were taken into account by examiners in determining grade boundaries. He said that there were few complaints about GCSE French.